1. Field of Invention
The invention relates to broadband communication networks and in particular to broadband communication networks utilizing coaxial cable.
2. Related Art
The worldwide utilization of external television (“TV”) antennas for receiving broadcast TV signals, and of cable TV and satellite TV is growing at a rapid pace. These television signals from an external TV antenna, cable TV and satellite TV (such as from direct broadcast satellite “DBS” systems) are usually received externally to a building (such as a home or an office) at a point-of-entry (“POE”). There may be multiple TV receivers and/or video monitors within the building and these multiple TV receivers may be in signal communication with the POE via a broadband cable network that may include a plurality of broadband cables and broadband cable splitters. Generally, these broadband cable splitters distribute downstream signals from the POE to various terminals (also known as “nodes”) in the building. The nodes may be connected to various types of customer premise equipment (“CPE”) such as cable converter boxes, televisions, video monitors, cable modems, cable phones and video game consoles.
Typically, these broadband cable networks are implemented utilizing coaxial cables and coaxial cable splitters, respectively. Additionally, in the case of cable TV or satellite TV, the multiple TV receivers may be in signal communication with the broadband cable network via a plurality of cable converter boxes, also known as set-top boxes (“STBs”), that are connected between the multiple TV receivers and the broadband cable network via a plurality of network nodes.
Typically, a STB connects to a coaxial cable from a network node (such as the wall outlet terminal) to receive cable TV and/or satellite TV signals. Usually, the STB receives the cable TV and/or satellite TV signals from the network node and converts them into tuned TV signals that may be received by the TV receiver and/or video signals that may be received by a video monitor.
In FIG. 1, an example known broadband cable network 100 (also known as a “cable system” and/or “cable wiring”) is shown within a building 102 (also known as customer premises or “CP”) such as a typical home or office. The broadband cable network 100 may be in signal communication with an optional cable service provider 104, optional broadcast TV station 106, and/or optional DBS satellite 108, via signal path 110; signal path 112, external antenna 114 and signal path 115; and signal path 116, DBS antenna 118 and signal path 119; respectively. The broadband cable network 100 also may be in signal communication with optional CPEs 120, 122 and 124, via signal paths 126, 128 and 130, respectively.
In FIG. 2, another example known broadband cable network is shown within a building (not shown) such as a typical home. The cable network 200 may be in signal communication with a cable provider (not shown), and/or satellite TV dish (not shown), and/or external antenna (not shown) via a signal path 202 such as a main coaxial cable from the building to a cable connection switch (not shown) outside of the building. The cable network 200 may include a POE 204 and main splitter 206, a sub-splitter 208, and STBs A 210, B 212 and C 214.
Within the cable network 200, the POE 204 may be in signal communication with main splitter 206 via signal path 216. The POE 204 may be the connection point from the cable provider, which is, located external to the building of the cable network 200. The POE 204 may be implemented as a coaxial cable connector, transformer and/or filter.
The main splitter 206 may be in signal communication with sub-splitter 208 and STB A 210 via signal paths 218 and 220, respectively. The sub-splitter 208 may be in signal communication with STB B 212 and STB C 214 via signal paths 222 and 224, respectively. The main splitter 206 and sub-splitter 208 may be implemented as coaxial cable splitters. The STBs A 210, B 212 and C 214 may be implemented by numerous well-known STB coaxial units such as cable television set-top boxes and/or satellite television set-top boxes. Typically, the signal paths 202, 216, 218, 220, 222 and 224 may be implemented utilizing coaxial cables.
In an example operation, the cable network 200 would receive CATV, and/or broadcast TV and/or satellite TV signals 226 via signal path 202 at the POE 204. The POE 204 may pass, transform and/or filter the received RF signals to a second RF signal 228 that may be passed to the main splitter 206 via signal path 216. The main splitter 206 may then split the second RF signal 228 into split RF signals 230 and 232. The split RF signal 230 is then passed to the sub-splitter 208 and the split RF signal 232 is passed to the STB A 210 via signal paths 218 and 220, respectively. Once the split RF signal 232 is received by the STB A 210, the STB A 210 may convert the received split RF signal 232 into a baseband or RF signal 238 that may be passed to a video monitor or a TV set (not shown) in signal communication with the STB A 210.
Once the split RF signal 230 is received by the sub-splitter 208, the sub-splitter 208 splits the received split RF signal 230 into sub-split RF signal 234 and 236 that are passed to STB B 212 and STB C 214 via signal paths 222 and 224, respectively. Once the sub-split RF signals 234 and 236 are received by the STB B 212 and STB C 214, the STB B 212 and STB C 214 may convert the received sub-split RF signals 234 and 236 into baseband or RF signals 240 and 242, respectively, that may be passed to video monitors or TV sets (not shown) in signal communication with STB B 212 and STB C 214, respectively.
Unfortunately, the cable network 200 may introduce significant losses from the POE 204 to STB A 210, STB B 212 and STB C 214 based on the quality of the splitters and coaxial cables. These losses may result in degraded signal levels at STB A 210, STB B 212 and STB C 214. In the past, while utilizing analog transmission schemes, these degraded signal levels usually resulted in some loss in reception quality at STBs as evidenced by such anomalies as ghost and noisy images on some attached video monitors or TV sets.
Unfortunately, these problems have become more important as many cable television providers transition from analog to digital transmissions. Unlike analog transmissions, digital transmissions do not gradually degrade with the transmission channel path performance. Typically, digital transmissions operate in an all or nothing fashion because if the performance of the transmission channel supports the digital transmission, the digital transmission is transmitted through the channel with sufficient quality that results in no visual degradation. Alternatively, if the performance of the transmission channel does not support the digital transmission, the digital transmission will transmit through the channel in a degraded fashion that may result in no video output at the corresponding STB.
Generally, the United States Federal Communication Commission (“FCC”) recommends that analog channels be transmitted at 0 dBmV power level at the TV set in order to produce high quality video signals. However, most cable providers currently transmit digital transmissions at lower power levels because digital transmissions are more robust.
Presently, many cable providers that transmit digital cable signals utilize quadrature amplification modulation (“QAM”) modulation schemes. Multi-level QAM modulation schemes are well known to those skilled in the art. Typically most cable providers that transmit digital cable signals utilize 64 QAM and 256 QAM modulation schemes and many cable providers are considering transmitting digital cable signals at 1024 QAM.
Unfortunately, digital modulation schemes only operate over channels that have good enough transmission performance capable of supporting the given digital modulation scheme. The higher the digital modulation scheme the higher the needed performance of the channel.
The coaxial cable distribution to a building is controlled by the cable company and typically conforms to well-defined criteria. The in-home cable distribution is typically provided by the homebuilder and is not well controlled, thus possibly resulting in a wide variation in reception. In a typical building 102 the performance of the coaxial cable depends on the coaxial cable distribution 110 and the performance of the building cable wiring in the broadband cable network 100. The measurement of the total signal performance is represented by the output power received at each node (not shown) connecting the broadband cable network 100 at the different CPEs (such as CPEs 120, 122 and 124). Typically, the output power at each node experiences a large amount of power variance from node to node that may be a result of the splitters and cables within the broadband cable network 100.
If the output power level at any node is below the needed power level to support the digital modulation scheme transmitted by the cable provider, the cable provider will have to remediate to ensure adequate performance. Usually, the output power level is measured as a signal metric such as the signal-to-noise ratio (“SNR” or “S/N”) of the received signal at the CPE attached at the node, or the received power level P.
As an example, in most cable set-top boxes (“STB”) used as a CPE, a 64 QAM modulation scheme typically requires about 23 to 24 dBmV SNR to operate. Similarly, 256 QAM requires about 30 to 32 dBmV and 1024 QAM requires about 36 to 38 dBmV.
If the SNR is not high enough to support the transmitted digital signal then the cable provider must remediate by means that include either amplifying the transmitted signal at the POE 204 or elsewhere, running new cable from the POE 204 to the node having the problem, or transmitting a lower order digital modulation scheme. Unfortunately, infrastructure remediation is difficult, time consuming, labor intensive and expensive.
As a result, many cable providers find it difficult to transmit higher than 64 or 256 QAM signals even though much of the cable plant might be able to support higher constellations. Unfortunately, the lower modulation scheme results in cable providers utilizing the cable bandwidth less efficiently. This results in a lower number of options for special unicast services such as cable modem applications and video on demand (“VoD”) services.
With the advent of cable modems and VoD, more and more end users are demanding these services. Cable providers, however, only have limited bandwidth to with which to operate.
Therefore, there is a need for a system and method to reduce the bandwidth limitations of the existing cable network for unicast applications such as cable modem and VoD transmission. Additionally, there is a need for a system and method to vary the digital modulation scheme for transmitting to each CPE in a cable network in order to optimize the cable provider's bandwidth.